Many
plants produce estrogen-like substances called phytoestrogens.
These plant estrogens can interfere with the interactions between
mammalian estrogens and their estrogen receptors (see Our Stolen
Future, Chapter 5). Industry flacks have claimed that the volume
of phytoestrogens in the human diet is so large compared to synthetic
estrogens that any worry about contaminants is misguided.

Their
argument fails on several grounds. First, it fails because much,
but not all, of the exposure to synthetic hormone disruptors is
not dietary. Their argument is irrelevant to non-dietary exposures.
Second, it fails because it completely ignores
the fact that many hormone disruptors interfere with hormones other
than estrogen.

And
finally, it fails even within the realm of dietary exposure to estrogen-like
compounds. It turns out that the body is quite capable of avoiding
the impact of many (but not all) phytoestrogens because we have
evolved defenses to cope with them.

In
fact,
the crucial distinction is not whether a compound is a plant vs.
a synthetic estrogen. Instead the focus should be on two issues:

Does
a specific estrogen like substance overcomes the body's physiological
defenses?

Does
it persist and bioaccumulate?

These
two questions together determine whether the levels of a given chemical,
plant-based or synthetic, will reach levels within the fetus that
are physiologically relevant, i.e., will they interfere with natural
hormone signalling crucial for the process of development.

About
the body's physiological defenses:People
possess chemical defenses which protect against at least some endocrine
disruptors, natural or synthetic. But of the endocrine disruptors
that have been studied carefully, the natural compounds are more
likely to be taken out of circulation by the body's defenses. Some
plant compounds are not eliminated or detoxified (see Our Stolen
Future, chapter 5). Some synthetic are neutralized. But the synthetic
compounds are more likely to make it through the bodies defenses.
This is likely due to the fact that humans have co-evolved with
many phytoestrogens, and in the process developed defenses.

About
bioaccumulation and persistence:Persistent
synthetic endocrine disruptors accumulate in body tissue to levels
that are orders of magnitude of times higher than observed levels
for phytoestrogens, and some are then transferred to the developing
fetus. The half-life (an estimator of how long a molecule of a compound
will persist) of DDT or DDE in the body, or of PCBs, is measured
in years and decades. The half-life of plant phytoestrogens is measured
in minutes and hours. Under normal circumstances, most plant phytoestrogens
don't stick around long enough or accumulate to high enough levels
within the fetus to cause problems. There are exceptions, and these
can be as important as the impact of synthetic compounds. But their
impact doesn't diminish the attention that should be paid to what
synthetic compounds can do.

Continuing research into this issue will
no doubt reveal a far more complex picture concerning natural defenses
vs. synthetic and natural hazards. Indeed, a key part of
the ongoing research will explore why the body's defense mechanisms
are effective against some but not all compounds. While far from
the final word, these new results do, however, counter the claim
that the presence of plant estrogens in the human diet is sufficient
reason to dismiss concern about synthetic compounds. It is clearly
not.